internal memory leak?

Ok so I wiped and flashed fresh 2.1.2 and initiaagly it gave me about 90mb free after a clean and fresh install. after i installed all my apps i still had about 70mb left. but during the past few days I've noticed the internal memory slowly decreasing or leaking eventhough I haven't downloaded anything new...I've lost about 10mb by doing absolutely nothing...what the hell is going on?

When you use some apps like a web browser, cache is stored to help things run faster. This takes up space. You can clear chache using the app manager or look in the app settings or use a cache clearing app.

I use Advanced Task Killer all the time, pretty much any time I pick up the phone.
When the phone has been running for a long time the memory it releases gradually decreases. There is a memory leak, but where?
Only reboot gets all the memory back.